The methods and findings arising out of Grant NS 07755 will be applied to investigating the plasticity of the human spinal cord which has been chronically transected at a cervical level. The goal of this research program is to reveal the principles and techniques by which programmed afferent stimulation, acting upon the inherent plasticity of the isolated spinal cord, can be used to control physiological systems innervated by the spinal cord distal to the transection. In two of the three studies concerned with the habituation process, predictions from a dual-process theory of habituation will be tested. The third study is parametric in nature, and focuses upon the effects of relatively lengthy interstimulus intervals on the habituation of both sympathetically mediated skin conductance responses and flexor reflexes controlled by the cervically transected spinal cord. The proposed classical conditioning studies are characterized by efforts to achieve: 1) adequate control procedures for distinguishing conditioning and pseudo- conditioning effects, 2) a judicious initial selection of conditioning arrangements with a reasonable likelihood of producing positive results, and 3) an explicit strategy for modifying procedures which prove to be unsuccessful and for following up results wich appear encouraging. The proposed avoidance learning study will involve yoked control procedures which have been used successfully in spinal animal studies.